I suggest that...

Group DOIs with case insensitive comparison to resolve works duplication / not grouping

I think that when comparing the DOIs of works to decide what to group, you aren't parsing them to be case insensitive using ASCII case folding for comparison of text.
https://www.doi.org/doi_handbook/2_Numbering.html#2.4The doi:10.1002/14651858.CD001730.pub3 is equivalent to doi:10.1002/14651858.cd001730.pub3
but Scopus and CrossRef are using these two different presentations, which then list as separate works in ORCID.
Although in this this case I can create a manual entry with the Scopus ID and the DOI as listed by CrossRef, I shouldn't have to and the Scopus presentation of the DOI is the one preferred by the publisher.

We are pleased to share that we have added a normalization option in the Registry as a part of our API 3.0 work. This allows identifiers which are case insensitive, such as DOIs, to be processed as the same regardless of case on the ORCID record. Therefore, they are grouped as expected. You can find the card with the update on our current development Trello, or view your ORCID record for an example if this issue has affected you previously: https://trello.com/c/5p6QK7bS/4254

Let us know if you find case sensitive identifiers which are not grouping on your record as expected.

We are pleased to share that we have added a normalization option in the Registry as a part of our API 3.0 work. This allows identifiers which are case insensitive, such as DOIs, to be processed as the same regardless of case on the ORCID record. Therefore, they are grouped as expected. You can find the card with the update on our current development Trello, or view your ORCID record for an example if this issue has affected you previously: https://trello.com/c/5p6QK7bS/4254

Currently the ORCID Registry processes all identifiers as being case sensitive. This is a known issue — some identifiers are case sensitive, whilst others are not.

Our team recognize this issue and will be addressing it by cataloguing our identifiers, their case sensitivity, and other validity issues, then putting these into effect and potentially sharing some of the data in the identifiers API (https://pub.orcid.org/v2.0/identifiers/ ).

We currently have looking into the identifiers scheduled to commence April 2017 and shall update you when we are further into the project.

Currently the ORCID Registry processes all identifiers as being case sensitive. This is a known issue — some identifiers are case sensitive, whilst others are not.

Our team recognises this issue and plans to address it by cataloguing our identifiers and their case sensitivity as one of the projects following the release of API 2.0. Expect to see more information from us on this in 2017.

I vote for ignoring "case" in DOIs. We just discovered that DataCIte has changed their case from all upper case now to lowercase when reporting to ORCID. So some of my works I gathered in June from DataCite match duplicate records, but now new DataCite records (reported in October) do not (all that is different is the change to lower case in the DOI).

When updating an ORCID record from various literature sources like Scopus, CrossRef, own entries, Pure, it happens easily that duplicates are not automatically being detected and hidden in the public view. Instead, you have to manually go through the list and hide duplicates. Only, if records contain the same doi the deduplication works.
Could this please be improved? Please try to establish a robust deduplication algorithm.